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T-cell and cytokine responses in leishmaniasis
T-cell
and cytokine
responses
in leishmaniasis
Steven G. Reed and Phillip Seattle Biomedical Research Institute, intracellular
Seattle and University
pathogens,
macrophages,
particularly
represent
unique
Leishmania are protozoan phages
and
responses.
are thus
parasites
T cell responses with
Leishmania.
T helper
type
2 responses
or absent
are have
replicate to
the
lymphocytes immune
exclusively influence
in determining
murine been
type
of Pennsylvania,
inhabit to
position
critical
In both
T helper
that
that
in an excellent
infections decreased
those
challenges
Scott
and
human
associated
2 response
with
has been
the
Philadelphia,
USA
and
system. in macro-
lymphocyte outcome
infections, disease, associated
of
strong and
a
with
healing.
Current
Opinion
in immunology
Introduction leishmanial infections range from self-healing cutaneous to uncontrolled diffuse cutaneous disease, from mild to highly destructive mucosal disease, and from subclinical to fatal systemic visceral disease. Patients with active visceral leishmaniasis lack Lez%mania-specific delayed hypersensitivity responses during acute disease, when specific antibody titers are high, and their lymphocytes fail to proliferate to the parasite in vitro. After resolution of symptoms, lymphocytes proliferate and produce cytokines in vitro in response to leishmanial antigens [ 11. Although leukopenia occurs in patients with acute visceral leishmaniasis, there may or may not be a severe reduction in circulating lymphocyte numbers, indicating that the depressed responsiveness is not due merely to the lack of available lymphocytes. Clinical
A different immunological picture is associated with cuta neous leishmaniasis. Strong delayed hypersensitivity and in vitro proliferative responses occur both during disease and after healing. At the other end of the immunologi cal spectrum is dilfuse cutaneous leishmaniasis, characterized by uncontrolled cutaneous lesions and significant Leishmunia-specific antibody production in the absence of T-cell proliferation or delayed hypersensitivity responses to the parasite. Mucosal leishmaniasis is frequently refractory to treatment and may be persistent or recurrent. With active mucosal disease, the intradermal skin test and lymphocyte proliferative responses are often exaggerated. The pathogenesis of the mucosal lesions may result from a hypersensitivity reaction to Leisb mania, which may explain some of the features of the disease such as the destructive attack on host tissue and the relative paucity of parasites in mucosal lesions. Although mouse models do not faithfully reproduce the range of clinical leishmaniasis they have provided im-
1993, 5:524-531
portant insights into immunoregulation in leishmaniasis, particularly with regard to the role of T-cell subsets and cytokine production in determining disease outcome.
Regulation
of T helper ceil subset
differentiation
in experimental
leishmaniasis
The immunological responses associated with susceptibility to Leishamia major have been extensively studied over the last decade [2]. In most mouse strains (e.g. C3H/HeN and C57BIJ6) this parasite causes a selfhealing’lesion, whereas in BALB/c mice the infection is progressive and eventually fatal. The nature of the T-cell response determines the outcome of infection. CD4+ T cells mediate both resistance or susceptibility following a primary L. major infection, whereas CD8+ T cells play a limited role in controlling disease [ 21. In contrast, CD8+ T cells may be as important as CD4+ T cells in mediating resistance to reinfection with L. major and Lehhnunia donovuni [3*,4*]. Finally, it has also been discovered that L. major infection induces significant proliferation of the y6 T cell population, although it remains unclear how these cells influence disease progression [5*]. CD4+ T cells can be separated into subsets based upon the repertoire of cytokines produced following stimulation [6]. T helper type 1 (Thl) cells produce interferon (IFN)-y and primarily mediate cell-mediated immunity, whereas T helper type 2 (Th2) cells produce interleukin (IL)-4, IL-5 and IL-10 and mediate humoral immunity. It is now known that the outcome of L. major infection in mice is dependent upon which of these Cl%+ T cell subsets predominates: Thl cell development leads to resistance, whereas Th2 cells confer susceptibility [7]. Not
Abbreviations CM-CSF-granulocyte-macropahge colony-stimulating factor; HSP-heat shock protein; ICAM-intercellular adhesion molecule; IFN-interferon; IL-interleukin; mA&monoclonal antibody; NK-natural killer; PBMC-peripheral blood mononuclear cell; SCl(tsevere combined immunodeficient; TCR-T-cell receptor; TGF--transforming growth factor; Th-T helper.
524
@
Current Biology Ltd ISSN 0952-7915
T-cell
The influence
of cytokines
in the development
cell subsets
The cytokine milieu at the time of parasite infection is critical in directing Th-cell subset differentiation (Table 1, Table 2). For example, treatment of resistant mice with anti-IFN-y monoclonal antibody (mAb) ablates Thl-cell development, and promotes Th2-cell expansion [lo]. Furthermore, it was found that transfer of T cells from Table
1. Some
of the known
roles of cytokines
nn resistance
IFN-y
Curative in viva
effects
Yes 158.601
killing
CM-CSF
Yes (R Badaro unpublished
Intracellular
and susceptibility
Yes 1531
in human
M-CSF
IL-3
Yes I611
Yes (481
responses
in leishmaniasis
Reed and Scott
BALB/c mice into severe combined inlnrurloclefi~iel~~ (SCID) mice rendered them resistant [11-l; resistance was dependent upon the development of Thl cells, which could be blocked by in zv’rtoadministration of anti-IFN-y mAb. In contrast, treatment of susceptible mice with anti-IL-4 mAb inhibits Th2-cell expansion, leading to Thl-cell development [ l2*,l3], However, whereas administration of IFN-y or IL-4 enhanced Thl~ and Th2-cell development, respectively, the changes were transient [ 141. This might be due to the rapid elimination of the recombinant cytokines. Thus, in a mouse strain not-mall> resistant to L. major, the stable transgenic introduction of IL-4 enhanced susceptibility [IS*]. When a L. mujo? clone that was transfected with IFN-y was used to initiate infection in nude mice, a slower progression of disease was observed, although in BALB/‘c mice the transfected L. major clone was unable to influence the development of Th2 cells or susceptibility [16*]. The limited capacity of IFN-y or IL-4 by themselves to permanently switch the Th cell subset phenotype suggests that while these cytokines may be required in Thl- or Th2-cell differentiation, they may not be sufficient, and that other cytokines or factors may modulate Th cell subset development.
all susceptibility, however, is related to the presence of Th2 cells. In some infections susceptibility is associated with an insufficient Thl response, rather than a dominant Th2 response. L donovuni infection in mice is one example [8]. Similarly, the inability of strains of mice resistant to L major to resolve lesions initiated by Leisb mania amuzonensb appears to be due to the absence of a Thl response, rather than to the dominance of Th2 cells [PI. These observations raise two questions: first, what factor(s) determine which T-cell subset predominates following infection; and second, how do cytokines, either T-cell or non-T-cell derived, modulate the ability of macrophages to eliminate the parasite.
of T helper
and cytokine
As IFN-y and IL-4 are required for Th cell subset development, they should be present soon after infection. In fact, lelshmanlasis.
IL-2
IL-4
IL-10
TNF-a
AL-10
IL-2 receptor
et al., data)
Yes 156,611
of
Leishmania Associated
wth
Yes [38.,39-l
Yes 135,36°,3901
healing Restores cO”nt
leukocyte
Yes (R Badaro et al,
in v&o
Restores
unpublished
data)
T cell
Yes I39.1
responses
,” vitro
Associated
with
Yes [35,38.,39.1
macrophage
colony-stimulating
Yes 135,36°,3901
Yes [35.36*.39*1
Yes 135.36*,38*,39*1
Yes 140,411
Yes [62,641
disease
M-CSF,
factor;
TNF,
tumor
necrow
factor.
--___ Table 2. Some of the known
roles of cytokines
IFN-y
CM-CSF
in resistance
IL-3
and susceptlblity
IL-2
I” munne
IL-4
lelshmaniasls.
IL-10
IL-12
TNF-b -.
Curative in viva
effects
Intracellular
Yes [%I
Yes 122*,23*1
Yes 1541
TCF-@
x-IL-4
?-II ~2
7 1(&P
___ Yes 1591
Yes 17.13.141
ie,
i24.1
Yes [591
kilkng of
Leishmania Associated
with
Yes l7.10,18*1
Yes L7.631
Yes 122=,23*1
Yes 1591
Yes l7.13.141
YPS 1171
Yea 124.1
Yes 1171
Yes 124.1
healing Thl-promoting
Yes [10,18*]
Yes [651
Yes 122*,23*1
ThZ-promoting Associated
Yes [171
with
Yes [571
disease
TNF,
tumor
necrosis
factor
Yes Cl71
Yes I24*.25*1 Yes [7,12*,631
Yes [631
Yes 124*,25*1
525
526
Immunity to infection
as early as 3 days after infection, enhanced IL-4 production is observed in the lymph nodes draining the infection site of susceptible mice, and IFN-?/is present in the lymph nodes from the resistant C3H/HeN mouse strain [lo]. In both strains, IL-2 is present at this early time. In BALB/c mice the IL-2 appears to be required for the development of the Th2-cell response, as animals treated continuously with anti-IL-2 mAb control their infection [ 171. In C3H/HeN mice natural killer (NK) cells appear to be the major source of IFN-y during the first few days of infection [US*]. However, whereas L. major was able to activate NKcells in vitro [ 11.1, L. donovuni could not [ 191, suggesting that differences in the parasite itself may iniluence NK-cell activation. The induction of this NKcell response is likely to be linked to IL-12, a cytokine produced by macrophages and B cells, that induces proliferation and IFN-y production by both NK and T cells [ 201. A central role for IL-12 in Thl-cell development is indicated by a recent study showing that macrophages infected with Listeria can bias the differentiation of naive T cells towards the Thl-cell phenotype, and that this effect is mediated by IL-12 [ 211. In L. major infections, systemic administration of IL-12 to BALB/c mice was found to enhance Thl-cell development, and promote healing [ 22*,23*]. This is the first demonstration that systemic administration of any cytokine can have a therapeutic effect in this disease. The factors controlling IL-12 production following leishmanial infection, as well as the potential of IL-12 as an immunopotentiator in vaccine-induced immunity, is currently an active area of investigation in several laboratories. In contrast to the positive signals IL-12 provides, transforming growth factor (TGF)-j!l appears to be important in downregulating protective responses. Active TGF-P was found to be produced following in vitro or in vivo infection with Leishmaniu [ 24.1. Administration of antiTGF-P mAb decreased IL-4 production, enhanced IFN-y production and promoted resistance to L. amazonensis in normally susceptible BALB/c mice [24*]. Interestingly, BALB/c mice injected with TGF-P and Leisb munia braziliensis, which normally fails to induce disease in mice, led to lesion development, suggesting that TGF-p may play a major role in the pathogenesis of cutaneous leishmaniasis [25*]. This was further supported by the findings that levels of active TGF-B produced following infection in vitro correlated with parasite strain virulence, and that local injection of TGF-j3 could activate lesion development in a quiescent L. braziliensis infection [25*]. Among the relevant effects of TGF-j3 on immune function is inhibition of macrophage activation by cytokines such as IFN-)I. Whereas an early bias in the immune response towards the Thl-cell phenotype is observed in C3H/HeN mice, other strains of mice that eventually control L major infections exhibit a mixed phenotype. For example, limiting dilution analysis of T-cell clones in ~57B1/6 mice during the first few weeks of infection demonstrated that both Thl and Th2 cells were present [26-l. Interestingly, infection with L major in this strain fails to induce the early NKcell response seen in C3H/HeN mice [ 18.1. At present, the factor(s) leading to the eventual dominance
of Thl cells in these animals are unknown. However, similar to C3H/HeN mice, resistance and Thl-cell differentiation are dependent on IFN-y [13].
Other
factors influencing
T helper
cell
development Several other factors may influence which T-cell subset dominates after Leisbmaniu infection, including the type of antigen-presenting cell, the nature of the antigens recognized and the parasite dose. Epidermal dendritic cells (Langerhans cells) were found to be efftcient antigenpresenting cells for leishmanial-specific T cells [ 271, and moreover Langerhans cells were found to be parasitized following in vivo infection with L. major [28*]. While there is no evidence that these cells bias which Th-cell subset dominates, they may process leishmanial antigens for early recognition at the lesion site. More critical for influencing Th-cell subset development may be differences in MHC class II interactions with the T-cell receptor (TCR). Thus, when mice that lacked the I-E region of the MHC and mice in which the I-E molecule was transgenically introduced were infected with L donovani, the introduction of the I-E region of the MHC was found to enhance parasite growth [29-l. Because Leisbmania live within macrophages, there has been considerable interest in evaluating the antigen-presenting capacity of such infected cells. It has been shown that L. donovuni infection downregulates MHC class II expression, which occurs at the level of gene transcription [30]. Other studies suggest that Leishmania-infected macrophages may be impaired in their ability to present antigens due to the inability to load MHC class II molecules with antigen [31 I. It is clear that certain pathogens are associated with preferential induction of certain Th-cell subsets. However, such preferential development is unlikely to be due to differences in the epitopes recognized by the TCR. For example, it was found that L. major infection of both resistant and susceptible mouse strains leads to the preferential expansion of Vp4, V,S TCRs [32*]. In addition, Tcell clones with a Thl or a Th2 phenotype were identified that had identical TCRs. Nevertheless, other characteristics of the antigen may bias the selection of a particular T-cell subset. One of the most important influences on the nature of the immune response in leishmaniasis may be the parasite dose. When guinea pigs are infected with 105 or 106 Leishnania enraktti they develop a self-healing lesion, whereas higher doses lead to uncontrolled metastatic spread of the parasites [ 331. More recently, it was demonstrated that very low doses of L major in BALB/c mice not only failed to initiate lesion development, but provided resistance to reinfection with higher doses [34]. Associated with resistance was the induction of protective cell-mediated immunity, suggesting that more consideration should be given to the doses of antigen used for immunization.
T-cell
Cytokine
profiles
in leishmaniasis
patients
Attempts to correlate Thl cytokines with various clinical forms of cutaneous and mucosal leishmaniasis have revealed a largely mixed cytokine profile, with the suggestion that IL-2 and IFN-), are associated with a controlled infection or healing response in cutaneous leishmaniasis [35,36*]. Perhaps the clearest correlation was the predominance of Th2 cytokine patterns in lesions of patients with diffuse cutaneous leishmaniasis [36*]. In a related study, the role of Iangerhans cells in the manifestation of various forms of cutaneous leishmaniasis was addressed [37]. A correlation was made between Iangerhans cell accumulation and the expression of HLADR and intercellular adhesion molecule (ICAM)- 1 in controlled, localized cutaneous lesions. In contrast, decreased Iangerhans cell accumulation and expression of HLA-DR and ICAMI was noted in lesions of diffuse cutaneous leishmaniasis patients. This study may suggest a role for Langerhans cells, which can be infected in vitro with Leishmania, and disease severity. Studies on cytokine patterns in various forms of cutaneous leishmaniasis are discussed further in the review by Modlin and Nutman in this issue (pp 511-517). The suggestion that Thl-cell responses were downregulated during visceral disease was first made in a report that demonstrated increased levels of serum IL-4 and IgE, and decreased levels of serum IFN-y in these patients [37]. More recent studies have directly addressed Thl and Th2 cytokine production by bone marrow and lymph node cells and peripheral blood mononuclear cells (PBMCS) during visceral leishmaniasis. Karp et al. [38*], observed increased levels of mRNA encoding IL-10 and IFN-y in bone marrow aspirates of patients with active disease, compared with levels in individuals treated with antimony. Ghalib et al. [39*], found mRNA encoding IL-10 in lymph nodes from patients with acute visceral leishmaniasis, but not in nodes of the same patients following successful chemotherapy. Abundant mRNA for IFN-)I was present in samples taken from patients both before and after therapy. IL-4 mRNA was also found to be increased in most samples taken before treatment but not in those taken after treatment. Of the cytokines so far examined, IL-10 was most clearly associated with pathology in visceral leishmaniasis. These in situ observations are likely to provide an accurate reflection of Leishmania-specific responses as bone marrow and lymph nodes are sites of parasite replication. In vitro studies further supported an important role for IL-10 in the regulation of T-cell responses in human leishmaniasis. Recombinant IL-10 completely blocked Leisbmania-driven proliferation of PBMCs from treated patients, and neutralizing anti-IL-10 mAb restored .Leishnunia-driven responses in PBMCs from acutely infected patients. Of particular interest, PBMCs from acutely infected patients, traditionally believed to be nonresponsive to antigens of Leisbmania, were found to produce IL-10 mRNA in a specific response to the parasite [39=].
and cytokine
responses
in leishmaniasis
Reed and Scott
The results obtained in patients with visceral leishmania~ sis suggest the possibility that IL-10 induced by infection can downregulate T-cell responses and lead to uncontrolled replication of the parasites in host macrophages. One mechanism may be by inhibiting IFN-y production. Although this was not supported by the demonstration that IFN-)I mRNA is present in samples taken from pa tients both before and after therapy, the possibility, that important effects on functional IFN-y may occur in the presence of increased IL-IO should not be discounted. Furthermore, neither the relative contributions of other cytokines on the intracellular control of Leishmaku ill zliuo nor the effects of IL-IO on the regulation of such cytokines, are known. Perhaps the most important influ ences of IL-10 on parasite replication, however, are mediated through effects on macrophage function. IL-10 is effective in blocking the intracellular killing of protozoa by macrophages and it is likely that this is the most im portant consequence of increased IL 10 in Lisceral leish maniasis. An interesting aspect that remains to be resolved is the source of IL-10 produced during visceral leishmaniasis. Several cell types, including macrophages, T cells and B cells, are capable of producing IL-IO. Although multiple cell types may be involved in the production of IL-IO during viscera1 leishmaniasis, the observation that PBMCs from patients, but not Leishmaniu-naive individuals, produced increased levels of R-10 after 4X hours of exposure in vitro to Leishmania [39-l may suggest that T cells can produce IL-10 in response to antigens. Other studies have suggested a role for soluble IL-2 rc~ ceptor in the immunopathology of visceral leishmaniasis. Elevated levels of soluble IL-2 receptor were reported to be a marker for active visceral leishmaniasis in patients from Brazil and the Mediterranean [40,41]. The presence of increased levels of IL2 receptor was indicated as at least one mechanism by which set-a from visceral leishmaniasis patients is able to downregulate normal T-cell proliferative responses. Another mechanism for this suppressive activity may be by the presence of serum IL-IO in patients with active disease [39-l. Two recent studies have addressed the importance of y6 T cells in several clinical forms of leishmaniasis [42,43*]. The reasons for the increase in circulating y6 T cells are not known. In both studies, y6 7‘ cells proliferated in z&o. It was shown that these cells responded to leishmania1 antigen, including a 70 kDa heat shock proteili (HSP) [43-l. An important immunopathological aspect of active visceral leishmaniasis is splenic hyperplasia, polyclonal Bcell activation and hypergammaglobulinemia. Factors responsible for these responses are not known. However, recent studies may provide some insight into the mechanisms for at least some aspects of the immune deregulation which may accompany the in ho proliferation of Letibmania. Two groups have described strong in vitro proliferative responses in human PBMCs from in dividuals not previously exposed to Leisbmania [ 44,451. Although at least one explanation for the stimulatoIy ef~ fects of Leisbmania antigens on T cells from uninfected
527
528
Immunity to infection
individuals is that it may reflect previous sensitization to a crossreacting (‘environmental) antigen, the kinetics of the proliferative response, peaking at 6-7 days as opposed to 5 days for a recall response to antigen, may suggest otherwise. From the studies on the responses of non-infected human PBMCs to antigens of Letimaniu and ttypanosomes, it is apparent that these responses are not unique to a single system and that they are not characteristic of either typical lectin or superantigen responses. It is not known through what means the T-cell proliferation occurs. These parasites appear to possess highly immunogenic molecules capable of stimulating the immune system in a way which results in undesirable Tcell responses, characterized by high antibody levels and diminished antigen-specific T-cell responses.
The role of cytokines macrophage
in controlling
activation
The principle effector mechanism mediating parasite elimination is the activation of macrophages, by IFN-)I for example. Production of cytokines that activate macrophages correlates with healing responses [46]. However, several other cytokines may also activate macrophages for leishmanicidal activity. Several cytokines exhibit a regulatory or inhibitory role in macrophage activation, including IL-4, IL-10 and TGF-p. It has been shown that treatment of murine macrophages with any one of these cytokines before exposure to IFN-y significantly reduces the microbicidal activity of Leisbmunia (reviewed in [47]). Some recent studies on interactions between Leisbmania and macrophages have emphasized the role of colony-stimulating factors in the activation of human monocytes and macrophages to inhibit the intra cellular replication of the parasite. A report on the ability of IL-3 to activate macrophage inhibition of Lekhnunia replication [481 adds to the previous observations of similar activities for other colony-stimulating factors, namely granulocyte-macrophage colony-stimulating factor (GMCSF) and macrophage colony-stimulating factor. The leishmanicidal stimulating activities of these molecules adds to their interest as candidates for therapeutics in leishmaniasis. An ongoing clinical trial using GM-CSF in combination with antimonial therapy has demonstrated the utility of this cytokine in rapidly reversing both leukopenia and thrombocytopenia associated with active visceral leishmaniasis (R Badaro, C Nascimento, JS Carvalho, F Badaro, JL Ho et al, unpublished data). As death due to visceral leishmaniasis is often associated with low white blood cell counts, with accompanying hemorrhage and secondary Infections, treatment with colony-stimulating factors appears to be a very promising therapeutic approach. It may be beneficial to combine colony-stimulating factors with IFN-y, which has already been shown to be useful in the therapy of visceral leishmaniasis, with the aim of achieving restoration of leukocytes and platelet numbers as well as macrophage activation.
Leishmania
infection
in immune
compromised
patients Prospective studies have demonstrated that the majority of human L. donovuni infections are subclinical or self-healing. Although the duration of positive skin test responses long after the cure of acute disease or the onset of subclinical infections has strongly suggested the persistence of live Lekbmunia, actual proof of dormant infection has come from studies of immunocompromised patients [49]. More recently Leishmuniu infection has been associated with AIDS, particularly in southern Europe [5&52]. Some cases have involved relapse of previous disease, but several others occurred in individuals with no previous history of leishmaniasis [52]. This latter observation underscores the importance of unapparent infections. Recurrence of cutaneous, as well as visceral disease, has been noted in AIDS patients. Antileishmanial antibodies, usually high in visceral leishmaniasis patients, are absent in a significant percentage of AIDS patients with L donovani infections. Cytokine responses are yet to be evaluated in these individuals. It is evident that leishmaniasis, both visceral and cutaneous, is emerging as an important opportunistic infection in AIDS patients.
Conclusion Experimental leishmanial infections have proven very useful models for investigating the regulation of cytokines and T-cell subsets during an infectious disease. Previous studies have established key roles for cytokines in determining the outcome of infection in mice. More recently, TGF-j3 has been identified as an important component in establishing leishmanial infection, and IL-12 as a cytokine involved in protection. Studies of visceral leishmaniasis in humans have, provided clear evidence for a immunoregu latoty role for IL-IO. Information from studying both experimental and clinical leishmaniases may be applicable to other diseases caused by macrophage pathogens.
References
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within
the annual
period
of
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3. .
T-cell strate the differences in the nature of the immune response required for primary resistance and that required for infection-induced immunity. 4. .
MURRAY HW, SQUIRES KE, MIRALLES CD, STOECKLE MY, GRANGER AM, GRANELL-PIPERNO A, B~CDAN C: Acquired Resistance and Granuloma Formation in Experimental Visceral Leishmaniasis. Differential T CeII and Lymphokine Roles in Initial Versus Established Immunity. J Immunol 1992, 148:185~1863. This study indicates that CD8+ T cells play an important role in resist tance to reinfection. ROSA~JP, MACDONAU)HR, LOUISJA: A Role for y6+ T Cells During Experimental Infection of Mice with Leishmaniu major. J Immunol 1993, 150:550-555. This is the first study to demonstrate that during murine leishmaniasis there is an expansion of y6 T cells. The expansion is seen after 2 weeks of infection, and is most pronounced in the BALB/c mice. What role these cells play in the infection remains unclear. 5. .
6.
MOSMANNTR, COFFMANRL: Thl and Tb2 Cells: Different Patterns of Lymphokine Secretion Lead to Different Functional Properties. Annu Reo Immunol 1989, 7:145-173.
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CHATEWN R, VARKI~AK, COFFMAN RL: IL-4 Induces a Th2 Response in Leishmania major-infected Mice. J Immunol 1992, 148:1182Z1187. This study demonstrates that IL-4 can prime in viva for a Th2 response, although IL-4 administration was insufficient to promote stable Th2 rep sponses in normally resistant mice. This study also demonstrates that whereas in viva administration of anti-IL~4 mAb leads to resistance in normaUy susceptible mice, simultaneous administration of anti-IFN-y mAb reversed the protective effects of IL-4 depletion, 13.
SADICK MD,
HEINZEL FP, HOLADAYBJ, Pu RT, DAWKINS RS, IOCKSLEYRM: Cure of Murine Leishmaniasis with Anti-Interleukin 4 Monoclonal Antibody. Evidence for a T Cell-dependent, Interferon-y-independent Mechanism. J Eq Med 1990, 171:115-127.
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LEALLM, Moss DW, KLIHNR, MULLERW, LIEWFY: Interleukin-4 Transgenic Mice of Resistant Background are Suscepti-
in leishmaniasis
Reed and Scott
ble to Leishmania major Infection. Eur J Immunol 1993. 23~566569. The 129/Sv mouse strain is resistant to L. major infection. In contrast. Il.-4 transgenic mice of this strain were susceptible, and developed un controlled lesions. These studies reinforce the fact that II.-+ is Important for the development of Th2 cells. TOBIN JF, RHNER SL, HATAM F, ZIIENC S. LWTAK CL, \X’II~!~ DF, UXXSLEY WI: Transfected Leishmania Expressing Biologically Active Interferon-y. ,/ lmmunol 1993, in press. This study is the first to transfect a cytokine gene into Lei.shnznnia. The data indicate that the presence of IFN-y atone is ins&i&m IO promote healing in BAIWc mice, although infection of nude mice v.~\ partlath attenuated. 16.
.
17.
HEINZEL FP,
RXRKO RM, ~%TA&IF, 1nc~s1.r:~ KM IL-2 is Necessary for the Progression of Leishmaniasis in Susceptible Murine Hosts. .I Immunol 1993, 150:3924-3931
SCHAWON TM, Sco’ri P: Natural Killer Cells are a Source of IFNy that Drives Differentiation of CD4 + T Cell Suhsets and Induces Early Resistance to Leishmania major in Mice. J Exp Med 1993, in press. In this study, it is shown that NK cells are a source of IFN y dunng the first few days of infection of C3H/HeN mice with 1. major; and that this NKceU response is associated with decreased number of parasites during the early stages of infection, and enhanced Thl~cell differentiation.
18. .
KAYEYPM, BA~XROFTGJ: Leishmania donovani Infection in Scid Mice: Lack of Tissue Response and in Vivo Macrophage Activation Correlates with Failure to Trigger Natural Wer Cell-derived y Interferon Production in Vitro. Infect Immun 1992, 60~4335-4342. Infection of SCID mice with L. donozmni leads to a progressive intcc tion. This study demonstrates that 1.. donotani fails to induce pro&c tion of IFN~y by NK cells, although in the presence of IL 2 low levels of IFN~y were detected. Interestingly, the authors found that L. dolonwc~~z amastigotes could inhibit IFN-y production induced by Lbterza 19. .
20.
TRJNCHIEN G,
D’ANDWA
A, RENGAUJII
M, VAUNTI:
NM.
Kr’rm
M, A.S:TEM, CHEHIMIJ: Natural Killer CeU Stimulatory Factor (NKSF) or Interleukin-12: A Heterodimeric Cytokine Produced by Accessory CeUs and with Regulatory Functions on T and NK Cell Responses. f+o~ Groufh I:uctor Rex19~13. in press.
11. .
VARK~IA K, CHATEWNR, LEALLMCC, COFFMANRL.: Reconstitution of C.B-17 Scid Mice with BALB/c T Ceils Initiates a T Helper Type-l Response and Renders Them Capable of Healing Leishmania major Infection. Eur J Immunoll993, 23~262.268. This study shows that transfer of T cells from BALB/c mice into SCID mice renders them resistant to L. major infection. As BALB/c mice are highly susceptible to L major infection, it might have been anticipated that these reconstituted mice would have also been susceptible. The authors show, however, that high levels of IFN-y appear to drive the naive T cells towards Thl cell development. The authors postulate that NK cells may participate in this response.
responses
21.
HSIEH
C S,
~~ACATONIA SE.
TRW
MIJRPIN KM Development of Thl IL-12 Produced by List&a-induced 1993, 260:547-549.
CS,
\xpm
SF,
O‘(;ZKK\
4.
CD4+ T Cells Through Macrophages CC~~m(’
SCI~OEXIAIT DS. RI~RKO KR4, KOSSER LE. C;AI.EI.\ MK: Recombinant Interleukin 12 Cures Mice Infected with Leishmania major. J Exp Med 1993, 177:1505-1509. IL-12 administered systemically during the first week of I. major Infcc tion in BALB/c mice promoted control of lesions and parasites. This is the first study to demonstrate that qtokine thcr;lpy c’an posltnrh intluence the outcome of a leishmanial infection.
22.
HEINZEL FP,
.
JP, CHUNG CL, MAYORSEI I, SLI~KA,%~Y&\~ Jhl, G(x.IJ%!.%\ SJ, SIER~IR~HDS, WOI.F SF, SC~TAI;RRG Resolution of Cuta neous Leishmaniasis: lnterleukin 12 Initiates a Protective Thl Immune Response. J EQ ‘Weed1993. in press. Describes results that are similar to those reported in thr stud>. ,)t IIeinzel el al. [22-l: IL~l2 can be protective when administcrcd at the time of L. mujor infection in BALB/c mice. The study ,also indicates that treatment of resistant mice with anti~IL 12 polyclonal antiserum cn hances disease. 23. .
24. .
SYPEK
BARR&NET~O M, BARRAL A, BROWNELL CE. SKEIKY YAW. ELLINGSWORTH IR, TWARDZIK DR, REED SG. Transforming Growth Factor-P in Leishmanial Infection: A Parasite Escape Mechanism. Science 1992, 257:545-548. This study shows that TGF-P contributes to the suscepubility of BALB c mice to infection with L amazonensis When mice were treated v&h anti-TGF-P mAb they were partially protected. In contrast, when TGF-P was administered with the parasite L. hrazilie?zsis, which normal& causes no disease in mice, lesion development wan observed.
529
530
Immunity to infection BARRAL A, BARRAI-NETTO M, YONG EC, BROWNELL CE, ‘IWARDZIK D, REEDSG: Transforming Growth Factor-P as a Virulence Mechanism for Leisbmania braziliensis. Proc Nat Acad Sci USA 1993, 90:3442-3446. In this paper, the authors demonstrate that macrophages infected with L braziliensisproduced active TGF-/3,and the amount produced correlated directlywith in vivovirulence. Of interest, quiescent L braziliensis infections were turned into active lesions by local administration of TGF-p. Exacerbation of infection by TGF-fl was associated with increased levels of IL~lOin the draining lymph node. 25.
35.
.
26. .
MORRISL, TROU?T AB, HANDMAN E, KELSOA: Changes in the Precursor Frequencies of IL-4 and IFN-y Secreting CD4+ Ceils Correlate with Resolution of Lesions in Murine Cutaneous Leishmaniasis. J Immunol 1992, 149:2715-2721. This paper shows that following infection of C57BI/6 mice both Thl and Th2 cells are present during the first few weeks of infection. Only after 2 weeks do Thl cells dominate, suggesting that a delayed mechanism exists which selects this phenotype. 27.
WIU 4 BUWK C, ROLLINGHOFF M, MOLL H: Murine Epidermal Langerhans Cells are Potent Stimulators of an Antigen-specific T CelI Response to Leishmania major, the Cause of Cutaneous Leishmaniasis. EurJ Immunoll992, 22:1341-1347.
28.
BLANKC, FUCHSH, MPERSBERGERK, ROLLINGHOFF M, MOLLH: Parasitism of Epidermal Langerhans Ceils in Experimental Cutaneous Leishmaniasis with Leisbmania major J Infect Dis 1993, 16741-25. In this manuscript, the authors demonstrate that Iangerhans cells are parasitized following infection with L major, thus implicating this antigen-presenting cell as a component in the initiation of an immune response M)leishmaniasis. .
KAYE PM, COOKE A, LUNDT, WAlTE M, BLACKWELL JM: AItered Course of Visceral Leishmaniasis in Mice Expressing Transgenic I-E Molecules. Eur J Immunoll992, 22:357-364. The course of L donovani infection in mice lacking the I-E region of the MHC (NOD mice) and NOD mice in which the I-E gene had been transgenically introduced was compared. The introduction of the I-E region of the MHC enhanced parasite growth, suggesting that differences at the level of antigen presentation may inlluence disease. 29. .
30.
KWAN WC, MCMA.!XERWR, WONG N, REINERNE: Inhibition of Expression of Major Histocompatibility Complex Class II Molecules in Macrophages Infected with Lefshmania donovani Occurs at the Level of Gene Transcription Via a Cyclic AMP-independent Mechanism. Infect Immun 1992, 60:2115-2120.
31.
FRUTHU, Souoz N, LOUISJ: Leishmania major Interferes with Antigen Presentation by Infected Macrophages. J Immunol 1993, 150:1857-l%&
32. .
REINER SL, WANGZ-E, HATAMF, SCOTT P, I~CKSLEYRM: Com-
mon Lineage of Thl and Th2 Subsets in Leishmaniasis. Science 1993, 259:1457-1460. In this manuscript the authors find that following infection with L. major mice exhibit a preferential usage of the Vo4, V,8 TCR. T-cell clones and hybridomas were isolated that utilize this TCR, and which have either the Thl or Th2 cytoklne phenotype. This study suggests that differences ln the dominance of Thl and Th2 cells is probably not related to recognition of dierent leishmanial antigens. 33.
34.
Pathogenesis 36. .
CACERES-DI’ITMAK G, TAP~A FJ, SANCHEZMA, YAMAMURAM, UVEMURAK, MODLIN RL, BUX)M BR, CONMT J: Detefmi-
nation of the Cytokine Profile in Leishmaniasis Using the Polymerase Exp Immunol 1993, 91:5C&505. These authors demonstrated that Th2 cytokines cosal lesions and in half of diffuse cutaneous weakly expressed in cutaneous lesions. 37.
American Cutaneous Chain Reaction. Clin were expressed in mulesions, but were only
ZW~NGENBERGER K, HARMSG, PEDROSA C, OMENAS, SANDKAMP B, NEIFERSK: Determinants of the Immune Response in
Visceral Leishmaniasis: Evidence for Predominance of Endogenous Interleukin 4 Over Interferon-y Production. Clin Immunol Immunopatbol 1990, 57:242-249. 38. .
KARP CL, El.-SAJISH, W~NN TA, SATI MMH, KORD~JANI HM, HA.!.HIMFA, HAG-AU M, NEVA FA, NUTMANTB, SACKSDL: In
Vivo Cytokine Profiles in Patients with Kala-azar. Marked Elevation of Both Interleukin 10 and Interferon-y. J Clin Invest 1993, 91:1644-1648. mRNAs encoding both IL-10 and IFN-y are present in bone marrow from kala-azar patients. GHAUB HG, PIWE~AM MR, SKEIKVYAW, SIDDIGM, HA~HIM FA, EL-HASSAN AM, Russo DM, REEDSG: Interleukin 10 Production Correlates with Pathology in Human Leisbmania Infections. J Clin Invest 1993, in press. donovani IL-10 mRNA was elevated in lymph nodes from patients with acute visceral leishmaniasis, and returned to negative levels following treatment. In contrast, IFN-y mRNA was elevated in samples from both acutely infected and convalescent patients PBMCs responded to leishmanial antigen in vitro by the production of IL-10 mRNA, IL-10 was able to 39. .
downregulate antigen-specific PBMC responses, and anti-IL-10mAb was able to restore proliferative responses to PBMCs from acutely infected patients 40.
BARRAI-NETTO M, BARRAL A, SANTOSSB, CARV~O EM, BADARO R, ROCHAH, REEDSG, JOHNSONWD JR: Soluble IL-2 Receptor as an Agent of Serum-mediated Suppression in Human Visceral Leishmaniasis. J Immunol 1991, 147~281-284.
41.
VITALE G,
42.
RA~IUDDIN S, TELMA%NIAW, EL-AWADMEH, AI-AMARI0, ALJANADIM: y6 T Cells and the Immune Response in Visceral
REINA G, MANSUETOS, MALTA R, GAM~INO G, MOCCIAROC, D’AGOSTINOR, DIEU M, CI~ E: The Significance of Serum Soluble IL-2 Receptor as a Marker for Active Visceral Leishmaniasis in Sicilian Patients. Clin Exp Immunol 1992, 90:21?222.
Leishmaniasis.
Eur J Immunol 1992, 22:1143%1148.
Russo DM, ARMITAGE RJ,BARR&NE’ITOM, BARRAL A, GRA~STEIN KH, &ED SG: Characterization of Circulating y6 T Cells in . Leishmaniasis Patients. J Immunol 1993, in press. Patients with a variety of clinical forms of leishmaniasis had elevated levels of circulating y6 T cells. These cells proliferated in vitro with 1eishmanIal antigen, and were found to respond to leishmanial HSP 70.
43.
44.
AKUFFOHO, BRI?TONSFF: Contibution of Non-Leisbmaniaspecilic Immunity to Resistance to Leishmania Infection in Humans. Clin Exp Immunol 1992, 87:58d4.
45.
KEMP M, HANSENMB, THEANDER TG: Recognition
of Leisb mania Antigens by T Lymphocytes from Nonexposed Individuals. Infect Immun 1992, 60:22462251.
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HOIADAYBJ, POMPEUMML, EVANST, BRAGADNM, TEXEIRAMJ, SOUSAAQ, SADICKMD, VA~CONCEL~S AW, ABRAMSJS, PERSON RD, IQXXEY RM: Correlates of Leisbmani~specilic Immunity in the Clinical Spectrum of Infection with Leisbmania cbagasi. J Infect Dk 1993, 167:411417.
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Ho JL, REED SG, SOBEL J, ARRUDAS, HE SH, WICK F%, GRABSTEINKH: Interleukin-3 Induces Antimicrobial Activ-
BRETXHERPA, WEI G, MENONJN, BIELEFELDT-OHMANN H: Es-
tablishment of Stable, Cell-mediated Immunity That Makes ‘Susceptible’ Mice Resistant to Leishmania major Science 1992, 257:53!+542. This study demonstrates that low challenge doses of L. major in the highly susceptible BALB/c mouse not only fail to initiate lesion development, but induce resistance to reinfection with high parasite doses. This study demonstrates the major but often ignored role that dose plays in determining the nature of the immune response.
of Human Leishmaniasis.
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R, VASSALLI P: Aggravation of Experimental Cutaneous Leishmaniasis in Mice by Administration of lnterleukin 3. Euv J Immunol 1988, l&1245-1251.
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EA, GIORDAYO .M Granuloqtc-
Factors mexicana
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HEINZI. FP, SAEUCKMD, MIKT~?ASS, 1ncltsi.r;~ RM: Production of IFN-), lnterleukin 2, Interleukin 4, and lntcrleukin 10 by in Vivo During Healing and ProgresCD4+ Lymphocytes sive Murine Leishmaniasis. Proc Nat1 Acad Sci I’SA 1991, 88:7011-7015.
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HO Jr., BAI)ARC) R, SCHWARI’XA, DlvAKlil.1.o CA, GEIFANI) JA, SO~BL J, BARRALA, BARF@&NEIXI M. C.~ALHO ELM, l&t) SG, JOHNSON WD, JR: Diminshed in Vitro Production of
MURRAYHW, STEIN J, WELTE K: Experimental Visceral Leishmaniasis: Production of Interleukin-2 and y Interferon, Tis-
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JL, REED SG, WICK
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and cytokine
65.
Factor-a During Acute After Therapy .I lr~fect
DOHER~ TM, COFFMAN RC: Immunization
with GMCSF-dcrived Macrophages Protects Susceptible Mice from ChalIenge with L. Major. J Immunol 1993. 150:230.
SG Reed, Seattle Biomedical Research Institute, 200, Seattle, Washington 98109~1651, USA.
+Nickerson Strccr. %utc
P Scott, Department of Pdthobiolo~. I Tniversity of Pennsylvania. \chool of Veterinary Medicine, 3800 Spmce Street, Philxlclphix Pw~rls~I\.mia 19104-6008, USA
531
and cytokine
responses
in leishmaniasis
Steven G. Reed and Phillip Seattle Biomedical Research Institute, intracellular
Seattle and University
pathogens,
macrophages,
particularly
represent
unique
Leishmania are protozoan phages
and
responses.
are thus
parasites
T cell responses with
Leishmania.
T helper
type
2 responses
or absent
are have
replicate to
the
lymphocytes immune
exclusively influence
in determining
murine been
type
of Pennsylvania,
inhabit to
position
critical
In both
T helper
that
that
in an excellent
infections decreased
those
challenges
Scott
and
human
associated
2 response
with
has been
the
Philadelphia,
USA
and
system. in macro-
lymphocyte outcome
infections, disease, associated
of
strong and
a
with
healing.
Current
Opinion
in immunology
Introduction leishmanial infections range from self-healing cutaneous to uncontrolled diffuse cutaneous disease, from mild to highly destructive mucosal disease, and from subclinical to fatal systemic visceral disease. Patients with active visceral leishmaniasis lack Lez%mania-specific delayed hypersensitivity responses during acute disease, when specific antibody titers are high, and their lymphocytes fail to proliferate to the parasite in vitro. After resolution of symptoms, lymphocytes proliferate and produce cytokines in vitro in response to leishmanial antigens [ 11. Although leukopenia occurs in patients with acute visceral leishmaniasis, there may or may not be a severe reduction in circulating lymphocyte numbers, indicating that the depressed responsiveness is not due merely to the lack of available lymphocytes. Clinical
A different immunological picture is associated with cuta neous leishmaniasis. Strong delayed hypersensitivity and in vitro proliferative responses occur both during disease and after healing. At the other end of the immunologi cal spectrum is dilfuse cutaneous leishmaniasis, characterized by uncontrolled cutaneous lesions and significant Leishmunia-specific antibody production in the absence of T-cell proliferation or delayed hypersensitivity responses to the parasite. Mucosal leishmaniasis is frequently refractory to treatment and may be persistent or recurrent. With active mucosal disease, the intradermal skin test and lymphocyte proliferative responses are often exaggerated. The pathogenesis of the mucosal lesions may result from a hypersensitivity reaction to Leisb mania, which may explain some of the features of the disease such as the destructive attack on host tissue and the relative paucity of parasites in mucosal lesions. Although mouse models do not faithfully reproduce the range of clinical leishmaniasis they have provided im-
1993, 5:524-531
portant insights into immunoregulation in leishmaniasis, particularly with regard to the role of T-cell subsets and cytokine production in determining disease outcome.
Regulation
of T helper ceil subset
differentiation
in experimental
leishmaniasis
The immunological responses associated with susceptibility to Leishamia major have been extensively studied over the last decade [2]. In most mouse strains (e.g. C3H/HeN and C57BIJ6) this parasite causes a selfhealing’lesion, whereas in BALB/c mice the infection is progressive and eventually fatal. The nature of the T-cell response determines the outcome of infection. CD4+ T cells mediate both resistance or susceptibility following a primary L. major infection, whereas CD8+ T cells play a limited role in controlling disease [ 21. In contrast, CD8+ T cells may be as important as CD4+ T cells in mediating resistance to reinfection with L. major and Lehhnunia donovuni [3*,4*]. Finally, it has also been discovered that L. major infection induces significant proliferation of the y6 T cell population, although it remains unclear how these cells influence disease progression [5*]. CD4+ T cells can be separated into subsets based upon the repertoire of cytokines produced following stimulation [6]. T helper type 1 (Thl) cells produce interferon (IFN)-y and primarily mediate cell-mediated immunity, whereas T helper type 2 (Th2) cells produce interleukin (IL)-4, IL-5 and IL-10 and mediate humoral immunity. It is now known that the outcome of L. major infection in mice is dependent upon which of these Cl%+ T cell subsets predominates: Thl cell development leads to resistance, whereas Th2 cells confer susceptibility [7]. Not
Abbreviations CM-CSF-granulocyte-macropahge colony-stimulating factor; HSP-heat shock protein; ICAM-intercellular adhesion molecule; IFN-interferon; IL-interleukin; mA&monoclonal antibody; NK-natural killer; PBMC-peripheral blood mononuclear cell; SCl(tsevere combined immunodeficient; TCR-T-cell receptor; TGF--transforming growth factor; Th-T helper.
524
@
Current Biology Ltd ISSN 0952-7915
T-cell
The influence
of cytokines
in the development
cell subsets
The cytokine milieu at the time of parasite infection is critical in directing Th-cell subset differentiation (Table 1, Table 2). For example, treatment of resistant mice with anti-IFN-y monoclonal antibody (mAb) ablates Thl-cell development, and promotes Th2-cell expansion [lo]. Furthermore, it was found that transfer of T cells from Table
1. Some
of the known
roles of cytokines
nn resistance
IFN-y
Curative in viva
effects
Yes 158.601
killing
CM-CSF
Yes (R Badaro unpublished
Intracellular
and susceptibility
Yes 1531
in human
M-CSF
IL-3
Yes I611
Yes (481
responses
in leishmaniasis
Reed and Scott
BALB/c mice into severe combined inlnrurloclefi~iel~~ (SCID) mice rendered them resistant [11-l; resistance was dependent upon the development of Thl cells, which could be blocked by in zv’rtoadministration of anti-IFN-y mAb. In contrast, treatment of susceptible mice with anti-IL-4 mAb inhibits Th2-cell expansion, leading to Thl-cell development [ l2*,l3], However, whereas administration of IFN-y or IL-4 enhanced Thl~ and Th2-cell development, respectively, the changes were transient [ 141. This might be due to the rapid elimination of the recombinant cytokines. Thus, in a mouse strain not-mall> resistant to L. major, the stable transgenic introduction of IL-4 enhanced susceptibility [IS*]. When a L. mujo? clone that was transfected with IFN-y was used to initiate infection in nude mice, a slower progression of disease was observed, although in BALB/‘c mice the transfected L. major clone was unable to influence the development of Th2 cells or susceptibility [16*]. The limited capacity of IFN-y or IL-4 by themselves to permanently switch the Th cell subset phenotype suggests that while these cytokines may be required in Thl- or Th2-cell differentiation, they may not be sufficient, and that other cytokines or factors may modulate Th cell subset development.
all susceptibility, however, is related to the presence of Th2 cells. In some infections susceptibility is associated with an insufficient Thl response, rather than a dominant Th2 response. L donovuni infection in mice is one example [8]. Similarly, the inability of strains of mice resistant to L major to resolve lesions initiated by Leisb mania amuzonensb appears to be due to the absence of a Thl response, rather than to the dominance of Th2 cells [PI. These observations raise two questions: first, what factor(s) determine which T-cell subset predominates following infection; and second, how do cytokines, either T-cell or non-T-cell derived, modulate the ability of macrophages to eliminate the parasite.
of T helper
and cytokine
As IFN-y and IL-4 are required for Th cell subset development, they should be present soon after infection. In fact, lelshmanlasis.
IL-2
IL-4
IL-10
TNF-a
AL-10
IL-2 receptor
et al., data)
Yes 156,611
of
Leishmania Associated
wth
Yes [38.,39-l
Yes 135,36°,3901
healing Restores cO”nt
leukocyte
Yes (R Badaro et al,
in v&o
Restores
unpublished
data)
T cell
Yes I39.1
responses
,” vitro
Associated
with
Yes [35,38.,39.1
macrophage
colony-stimulating
Yes 135,36°,3901
Yes [35.36*.39*1
Yes 135.36*,38*,39*1
Yes 140,411
Yes [62,641
disease
M-CSF,
factor;
TNF,
tumor
necrow
factor.
--___ Table 2. Some of the known
roles of cytokines
IFN-y
CM-CSF
in resistance
IL-3
and susceptlblity
IL-2
I” munne
IL-4
lelshmaniasls.
IL-10
IL-12
TNF-b -.
Curative in viva
effects
Intracellular
Yes [%I
Yes 122*,23*1
Yes 1541
TCF-@
x-IL-4
?-II ~2
7 1(&P
___ Yes 1591
Yes 17.13.141
ie,
i24.1
Yes [591
kilkng of
Leishmania Associated
with
Yes l7.10,18*1
Yes L7.631
Yes 122=,23*1
Yes 1591
Yes l7.13.141
YPS 1171
Yea 124.1
Yes 1171
Yes 124.1
healing Thl-promoting
Yes [10,18*]
Yes [651
Yes 122*,23*1
ThZ-promoting Associated
Yes [171
with
Yes [571
disease
TNF,
tumor
necrosis
factor
Yes Cl71
Yes I24*.25*1 Yes [7,12*,631
Yes [631
Yes 124*,25*1
525
526
Immunity to infection
as early as 3 days after infection, enhanced IL-4 production is observed in the lymph nodes draining the infection site of susceptible mice, and IFN-?/is present in the lymph nodes from the resistant C3H/HeN mouse strain [lo]. In both strains, IL-2 is present at this early time. In BALB/c mice the IL-2 appears to be required for the development of the Th2-cell response, as animals treated continuously with anti-IL-2 mAb control their infection [ 171. In C3H/HeN mice natural killer (NK) cells appear to be the major source of IFN-y during the first few days of infection [US*]. However, whereas L. major was able to activate NKcells in vitro [ 11.1, L. donovuni could not [ 191, suggesting that differences in the parasite itself may iniluence NK-cell activation. The induction of this NKcell response is likely to be linked to IL-12, a cytokine produced by macrophages and B cells, that induces proliferation and IFN-y production by both NK and T cells [ 201. A central role for IL-12 in Thl-cell development is indicated by a recent study showing that macrophages infected with Listeria can bias the differentiation of naive T cells towards the Thl-cell phenotype, and that this effect is mediated by IL-12 [ 211. In L. major infections, systemic administration of IL-12 to BALB/c mice was found to enhance Thl-cell development, and promote healing [ 22*,23*]. This is the first demonstration that systemic administration of any cytokine can have a therapeutic effect in this disease. The factors controlling IL-12 production following leishmanial infection, as well as the potential of IL-12 as an immunopotentiator in vaccine-induced immunity, is currently an active area of investigation in several laboratories. In contrast to the positive signals IL-12 provides, transforming growth factor (TGF)-j!l appears to be important in downregulating protective responses. Active TGF-P was found to be produced following in vitro or in vivo infection with Leishmaniu [ 24.1. Administration of antiTGF-P mAb decreased IL-4 production, enhanced IFN-y production and promoted resistance to L. amazonensis in normally susceptible BALB/c mice [24*]. Interestingly, BALB/c mice injected with TGF-P and Leisb munia braziliensis, which normally fails to induce disease in mice, led to lesion development, suggesting that TGF-p may play a major role in the pathogenesis of cutaneous leishmaniasis [25*]. This was further supported by the findings that levels of active TGF-B produced following infection in vitro correlated with parasite strain virulence, and that local injection of TGF-j3 could activate lesion development in a quiescent L. braziliensis infection [25*]. Among the relevant effects of TGF-j3 on immune function is inhibition of macrophage activation by cytokines such as IFN-)I. Whereas an early bias in the immune response towards the Thl-cell phenotype is observed in C3H/HeN mice, other strains of mice that eventually control L major infections exhibit a mixed phenotype. For example, limiting dilution analysis of T-cell clones in ~57B1/6 mice during the first few weeks of infection demonstrated that both Thl and Th2 cells were present [26-l. Interestingly, infection with L major in this strain fails to induce the early NKcell response seen in C3H/HeN mice [ 18.1. At present, the factor(s) leading to the eventual dominance
of Thl cells in these animals are unknown. However, similar to C3H/HeN mice, resistance and Thl-cell differentiation are dependent on IFN-y [13].
Other
factors influencing
T helper
cell
development Several other factors may influence which T-cell subset dominates after Leisbmaniu infection, including the type of antigen-presenting cell, the nature of the antigens recognized and the parasite dose. Epidermal dendritic cells (Langerhans cells) were found to be efftcient antigenpresenting cells for leishmanial-specific T cells [ 271, and moreover Langerhans cells were found to be parasitized following in vivo infection with L. major [28*]. While there is no evidence that these cells bias which Th-cell subset dominates, they may process leishmanial antigens for early recognition at the lesion site. More critical for influencing Th-cell subset development may be differences in MHC class II interactions with the T-cell receptor (TCR). Thus, when mice that lacked the I-E region of the MHC and mice in which the I-E molecule was transgenically introduced were infected with L donovani, the introduction of the I-E region of the MHC was found to enhance parasite growth [29-l. Because Leisbmania live within macrophages, there has been considerable interest in evaluating the antigen-presenting capacity of such infected cells. It has been shown that L. donovuni infection downregulates MHC class II expression, which occurs at the level of gene transcription [30]. Other studies suggest that Leishmania-infected macrophages may be impaired in their ability to present antigens due to the inability to load MHC class II molecules with antigen [31 I. It is clear that certain pathogens are associated with preferential induction of certain Th-cell subsets. However, such preferential development is unlikely to be due to differences in the epitopes recognized by the TCR. For example, it was found that L. major infection of both resistant and susceptible mouse strains leads to the preferential expansion of Vp4, V,S TCRs [32*]. In addition, Tcell clones with a Thl or a Th2 phenotype were identified that had identical TCRs. Nevertheless, other characteristics of the antigen may bias the selection of a particular T-cell subset. One of the most important influences on the nature of the immune response in leishmaniasis may be the parasite dose. When guinea pigs are infected with 105 or 106 Leishnania enraktti they develop a self-healing lesion, whereas higher doses lead to uncontrolled metastatic spread of the parasites [ 331. More recently, it was demonstrated that very low doses of L major in BALB/c mice not only failed to initiate lesion development, but provided resistance to reinfection with higher doses [34]. Associated with resistance was the induction of protective cell-mediated immunity, suggesting that more consideration should be given to the doses of antigen used for immunization.
T-cell
Cytokine
profiles
in leishmaniasis
patients
Attempts to correlate Thl cytokines with various clinical forms of cutaneous and mucosal leishmaniasis have revealed a largely mixed cytokine profile, with the suggestion that IL-2 and IFN-), are associated with a controlled infection or healing response in cutaneous leishmaniasis [35,36*]. Perhaps the clearest correlation was the predominance of Th2 cytokine patterns in lesions of patients with diffuse cutaneous leishmaniasis [36*]. In a related study, the role of Iangerhans cells in the manifestation of various forms of cutaneous leishmaniasis was addressed [37]. A correlation was made between Iangerhans cell accumulation and the expression of HLADR and intercellular adhesion molecule (ICAM)- 1 in controlled, localized cutaneous lesions. In contrast, decreased Iangerhans cell accumulation and expression of HLA-DR and ICAMI was noted in lesions of diffuse cutaneous leishmaniasis patients. This study may suggest a role for Langerhans cells, which can be infected in vitro with Leishmania, and disease severity. Studies on cytokine patterns in various forms of cutaneous leishmaniasis are discussed further in the review by Modlin and Nutman in this issue (pp 511-517). The suggestion that Thl-cell responses were downregulated during visceral disease was first made in a report that demonstrated increased levels of serum IL-4 and IgE, and decreased levels of serum IFN-y in these patients [37]. More recent studies have directly addressed Thl and Th2 cytokine production by bone marrow and lymph node cells and peripheral blood mononuclear cells (PBMCS) during visceral leishmaniasis. Karp et al. [38*], observed increased levels of mRNA encoding IL-10 and IFN-y in bone marrow aspirates of patients with active disease, compared with levels in individuals treated with antimony. Ghalib et al. [39*], found mRNA encoding IL-10 in lymph nodes from patients with acute visceral leishmaniasis, but not in nodes of the same patients following successful chemotherapy. Abundant mRNA for IFN-)I was present in samples taken from patients both before and after therapy. IL-4 mRNA was also found to be increased in most samples taken before treatment but not in those taken after treatment. Of the cytokines so far examined, IL-10 was most clearly associated with pathology in visceral leishmaniasis. These in situ observations are likely to provide an accurate reflection of Leishmania-specific responses as bone marrow and lymph nodes are sites of parasite replication. In vitro studies further supported an important role for IL-10 in the regulation of T-cell responses in human leishmaniasis. Recombinant IL-10 completely blocked Leisbmania-driven proliferation of PBMCs from treated patients, and neutralizing anti-IL-10 mAb restored .Leishnunia-driven responses in PBMCs from acutely infected patients. Of particular interest, PBMCs from acutely infected patients, traditionally believed to be nonresponsive to antigens of Leisbmania, were found to produce IL-10 mRNA in a specific response to the parasite [39=].
and cytokine
responses
in leishmaniasis
Reed and Scott
The results obtained in patients with visceral leishmania~ sis suggest the possibility that IL-10 induced by infection can downregulate T-cell responses and lead to uncontrolled replication of the parasites in host macrophages. One mechanism may be by inhibiting IFN-y production. Although this was not supported by the demonstration that IFN-)I mRNA is present in samples taken from pa tients both before and after therapy, the possibility, that important effects on functional IFN-y may occur in the presence of increased IL-IO should not be discounted. Furthermore, neither the relative contributions of other cytokines on the intracellular control of Leishmaku ill zliuo nor the effects of IL-IO on the regulation of such cytokines, are known. Perhaps the most important influ ences of IL-10 on parasite replication, however, are mediated through effects on macrophage function. IL-10 is effective in blocking the intracellular killing of protozoa by macrophages and it is likely that this is the most im portant consequence of increased IL 10 in Lisceral leish maniasis. An interesting aspect that remains to be resolved is the source of IL-10 produced during visceral leishmaniasis. Several cell types, including macrophages, T cells and B cells, are capable of producing IL-IO. Although multiple cell types may be involved in the production of IL-IO during viscera1 leishmaniasis, the observation that PBMCs from patients, but not Leishmaniu-naive individuals, produced increased levels of R-10 after 4X hours of exposure in vitro to Leishmania [39-l may suggest that T cells can produce IL-10 in response to antigens. Other studies have suggested a role for soluble IL-2 rc~ ceptor in the immunopathology of visceral leishmaniasis. Elevated levels of soluble IL-2 receptor were reported to be a marker for active visceral leishmaniasis in patients from Brazil and the Mediterranean [40,41]. The presence of increased levels of IL2 receptor was indicated as at least one mechanism by which set-a from visceral leishmaniasis patients is able to downregulate normal T-cell proliferative responses. Another mechanism for this suppressive activity may be by the presence of serum IL-IO in patients with active disease [39-l. Two recent studies have addressed the importance of y6 T cells in several clinical forms of leishmaniasis [42,43*]. The reasons for the increase in circulating y6 T cells are not known. In both studies, y6 7‘ cells proliferated in z&o. It was shown that these cells responded to leishmania1 antigen, including a 70 kDa heat shock proteili (HSP) [43-l. An important immunopathological aspect of active visceral leishmaniasis is splenic hyperplasia, polyclonal Bcell activation and hypergammaglobulinemia. Factors responsible for these responses are not known. However, recent studies may provide some insight into the mechanisms for at least some aspects of the immune deregulation which may accompany the in ho proliferation of Letibmania. Two groups have described strong in vitro proliferative responses in human PBMCs from in dividuals not previously exposed to Leisbmania [ 44,451. Although at least one explanation for the stimulatoIy ef~ fects of Leisbmania antigens on T cells from uninfected
527
528
Immunity to infection
individuals is that it may reflect previous sensitization to a crossreacting (‘environmental) antigen, the kinetics of the proliferative response, peaking at 6-7 days as opposed to 5 days for a recall response to antigen, may suggest otherwise. From the studies on the responses of non-infected human PBMCs to antigens of Letimaniu and ttypanosomes, it is apparent that these responses are not unique to a single system and that they are not characteristic of either typical lectin or superantigen responses. It is not known through what means the T-cell proliferation occurs. These parasites appear to possess highly immunogenic molecules capable of stimulating the immune system in a way which results in undesirable Tcell responses, characterized by high antibody levels and diminished antigen-specific T-cell responses.
The role of cytokines macrophage
in controlling
activation
The principle effector mechanism mediating parasite elimination is the activation of macrophages, by IFN-)I for example. Production of cytokines that activate macrophages correlates with healing responses [46]. However, several other cytokines may also activate macrophages for leishmanicidal activity. Several cytokines exhibit a regulatory or inhibitory role in macrophage activation, including IL-4, IL-10 and TGF-p. It has been shown that treatment of murine macrophages with any one of these cytokines before exposure to IFN-y significantly reduces the microbicidal activity of Leisbmunia (reviewed in [47]). Some recent studies on interactions between Leisbmania and macrophages have emphasized the role of colony-stimulating factors in the activation of human monocytes and macrophages to inhibit the intra cellular replication of the parasite. A report on the ability of IL-3 to activate macrophage inhibition of Lekhnunia replication [481 adds to the previous observations of similar activities for other colony-stimulating factors, namely granulocyte-macrophage colony-stimulating factor (GMCSF) and macrophage colony-stimulating factor. The leishmanicidal stimulating activities of these molecules adds to their interest as candidates for therapeutics in leishmaniasis. An ongoing clinical trial using GM-CSF in combination with antimonial therapy has demonstrated the utility of this cytokine in rapidly reversing both leukopenia and thrombocytopenia associated with active visceral leishmaniasis (R Badaro, C Nascimento, JS Carvalho, F Badaro, JL Ho et al, unpublished data). As death due to visceral leishmaniasis is often associated with low white blood cell counts, with accompanying hemorrhage and secondary Infections, treatment with colony-stimulating factors appears to be a very promising therapeutic approach. It may be beneficial to combine colony-stimulating factors with IFN-y, which has already been shown to be useful in the therapy of visceral leishmaniasis, with the aim of achieving restoration of leukocytes and platelet numbers as well as macrophage activation.
Leishmania
infection
in immune
compromised
patients Prospective studies have demonstrated that the majority of human L. donovuni infections are subclinical or self-healing. Although the duration of positive skin test responses long after the cure of acute disease or the onset of subclinical infections has strongly suggested the persistence of live Lekbmunia, actual proof of dormant infection has come from studies of immunocompromised patients [49]. More recently Leishmuniu infection has been associated with AIDS, particularly in southern Europe [5&52]. Some cases have involved relapse of previous disease, but several others occurred in individuals with no previous history of leishmaniasis [52]. This latter observation underscores the importance of unapparent infections. Recurrence of cutaneous, as well as visceral disease, has been noted in AIDS patients. Antileishmanial antibodies, usually high in visceral leishmaniasis patients, are absent in a significant percentage of AIDS patients with L donovani infections. Cytokine responses are yet to be evaluated in these individuals. It is evident that leishmaniasis, both visceral and cutaneous, is emerging as an important opportunistic infection in AIDS patients.
Conclusion Experimental leishmanial infections have proven very useful models for investigating the regulation of cytokines and T-cell subsets during an infectious disease. Previous studies have established key roles for cytokines in determining the outcome of infection in mice. More recently, TGF-j3 has been identified as an important component in establishing leishmanial infection, and IL-12 as a cytokine involved in protection. Studies of visceral leishmaniasis in humans have, provided clear evidence for a immunoregu latoty role for IL-IO. Information from studying both experimental and clinical leishmaniases may be applicable to other diseases caused by macrophage pathogens.
References
and recommended
Papers of particular interest, published raiew, have been highlighted as: . of special interest .. of outstanding interest
reading
within
the annual
period
of
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CARWHO EM, BAIXRO R, REED SG, JOHNSON WD, JONES TC: Absence of y Interferon and Interleukin-2 Production During Active Visceral Leishmaniasis. / Clin Invest 1985, 76:206&2069.
2.
IJEW FY: Induction, Regulation and Function of T-cell Subsets in Leishmaniasis. Cbem Immunol 1992, 54:117-135.
MULLERI: Role of T CeII Subsets During the Recall of Immunologic Memory to Leisbmania major Eur J Immunol 1992, 22:3063-3069. Resistance to reinfection with L. major in CBA/J mice was shown to be dependent upon both ClYi+ and CD8+ T cells. These studies demon-
3. .
T-cell strate the differences in the nature of the immune response required for primary resistance and that required for infection-induced immunity. 4. .
MURRAY HW, SQUIRES KE, MIRALLES CD, STOECKLE MY, GRANGER AM, GRANELL-PIPERNO A, B~CDAN C: Acquired Resistance and Granuloma Formation in Experimental Visceral Leishmaniasis. Differential T CeII and Lymphokine Roles in Initial Versus Established Immunity. J Immunol 1992, 148:185~1863. This study indicates that CD8+ T cells play an important role in resist tance to reinfection. ROSA~JP, MACDONAU)HR, LOUISJA: A Role for y6+ T Cells During Experimental Infection of Mice with Leishmaniu major. J Immunol 1993, 150:550-555. This is the first study to demonstrate that during murine leishmaniasis there is an expansion of y6 T cells. The expansion is seen after 2 weeks of infection, and is most pronounced in the BALB/c mice. What role these cells play in the infection remains unclear. 5. .
6.
MOSMANNTR, COFFMANRL: Thl and Tb2 Cells: Different Patterns of Lymphokine Secretion Lead to Different Functional Properties. Annu Reo Immunol 1989, 7:145-173.
7.
bcKSLEY RM, Scorn P: Helper T-cell Subsets in Mouse Leishmaniasis: Induction, Expansion and Effector Function. Immunol To&y 1991, 12A5%A61.
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KAYE PM, CURRYAJ, BIACKWEU.JM: Differential Production of Thl- and Th2-derived Cytokines Does Not Determine the Genetically Controlled or Vaccine-induced Rate of Cure in Murine Visceral Leishmaniasis. J Immunol 1991, 146:2763-2770.
&ONsO LCC, ScOTr P: Immune Responses Associated with the Susceptibility of C57BL/lO Mice to Leishmania amazonensis. Infect Immun 1993, in press. This study indicates that the inability of mice that are resistant to L major infection to heal following infection with L amazonens& is not related to enhanced Th2 responses. but rather appears to be due to the absence of a sufficient Thl response.
9. .
10.
SCOTT P: IFN-y Modulates the Early Development of Thl and Th2 Responses in a Murine Model of Cutaneous Leishmaniasis. J Immunol 1991, 147:314+3155.
and cytokine
12. .
CHATEWN R, VARKI~AK, COFFMAN RL: IL-4 Induces a Th2 Response in Leishmania major-infected Mice. J Immunol 1992, 148:1182Z1187. This study demonstrates that IL-4 can prime in viva for a Th2 response, although IL-4 administration was insufficient to promote stable Th2 rep sponses in normally resistant mice. This study also demonstrates that whereas in viva administration of anti-IL~4 mAb leads to resistance in normaUy susceptible mice, simultaneous administration of anti-IFN-y mAb reversed the protective effects of IL-4 depletion, 13.
SADICK MD,
HEINZEL FP, HOLADAYBJ, Pu RT, DAWKINS RS, IOCKSLEYRM: Cure of Murine Leishmaniasis with Anti-Interleukin 4 Monoclonal Antibody. Evidence for a T Cell-dependent, Interferon-y-independent Mechanism. J Eq Med 1990, 171:115-127.
14.
COFFMANRI+ VARKILAK, SCOTT P, CHATEWN R: Role of Cytokines in the DIlferentiation of CD4+ T-cell Subsets in Viva. Immunol Rev 1991, 123:18%207.
15. .
LEALLM, Moss DW, KLIHNR, MULLERW, LIEWFY: Interleukin-4 Transgenic Mice of Resistant Background are Suscepti-
in leishmaniasis
Reed and Scott
ble to Leishmania major Infection. Eur J Immunol 1993. 23~566569. The 129/Sv mouse strain is resistant to L. major infection. In contrast. Il.-4 transgenic mice of this strain were susceptible, and developed un controlled lesions. These studies reinforce the fact that II.-+ is Important for the development of Th2 cells. TOBIN JF, RHNER SL, HATAM F, ZIIENC S. LWTAK CL, \X’II~!~ DF, UXXSLEY WI: Transfected Leishmania Expressing Biologically Active Interferon-y. ,/ lmmunol 1993, in press. This study is the first to transfect a cytokine gene into Lei.shnznnia. The data indicate that the presence of IFN-y atone is ins&i&m IO promote healing in BAIWc mice, although infection of nude mice v.~\ partlath attenuated. 16.
.
17.
HEINZEL FP,
RXRKO RM, ~%TA&IF, 1nc~s1.r:~ KM IL-2 is Necessary for the Progression of Leishmaniasis in Susceptible Murine Hosts. .I Immunol 1993, 150:3924-3931
SCHAWON TM, Sco’ri P: Natural Killer Cells are a Source of IFNy that Drives Differentiation of CD4 + T Cell Suhsets and Induces Early Resistance to Leishmania major in Mice. J Exp Med 1993, in press. In this study, it is shown that NK cells are a source of IFN y dunng the first few days of infection of C3H/HeN mice with 1. major; and that this NKceU response is associated with decreased number of parasites during the early stages of infection, and enhanced Thl~cell differentiation.
18. .
KAYEYPM, BA~XROFTGJ: Leishmania donovani Infection in Scid Mice: Lack of Tissue Response and in Vivo Macrophage Activation Correlates with Failure to Trigger Natural Wer Cell-derived y Interferon Production in Vitro. Infect Immun 1992, 60~4335-4342. Infection of SCID mice with L. donozmni leads to a progressive intcc tion. This study demonstrates that 1.. donotani fails to induce pro&c tion of IFN~y by NK cells, although in the presence of IL 2 low levels of IFN~y were detected. Interestingly, the authors found that L. dolonwc~~z amastigotes could inhibit IFN-y production induced by Lbterza 19. .
20.
TRJNCHIEN G,
D’ANDWA
A, RENGAUJII
M, VAUNTI:
NM.
Kr’rm
M, A.S:TEM, CHEHIMIJ: Natural Killer CeU Stimulatory Factor (NKSF) or Interleukin-12: A Heterodimeric Cytokine Produced by Accessory CeUs and with Regulatory Functions on T and NK Cell Responses. f+o~ Groufh I:uctor Rex19~13. in press.
11. .
VARK~IA K, CHATEWNR, LEALLMCC, COFFMANRL.: Reconstitution of C.B-17 Scid Mice with BALB/c T Ceils Initiates a T Helper Type-l Response and Renders Them Capable of Healing Leishmania major Infection. Eur J Immunoll993, 23~262.268. This study shows that transfer of T cells from BALB/c mice into SCID mice renders them resistant to L. major infection. As BALB/c mice are highly susceptible to L major infection, it might have been anticipated that these reconstituted mice would have also been susceptible. The authors show, however, that high levels of IFN-y appear to drive the naive T cells towards Thl cell development. The authors postulate that NK cells may participate in this response.
responses
21.
HSIEH
C S,
~~ACATONIA SE.
TRW
MIJRPIN KM Development of Thl IL-12 Produced by List&a-induced 1993, 260:547-549.
CS,
\xpm
SF,
O‘(;ZKK\
4.
CD4+ T Cells Through Macrophages CC~~m(’
SCI~OEXIAIT DS. RI~RKO KR4, KOSSER LE. C;AI.EI.\ MK: Recombinant Interleukin 12 Cures Mice Infected with Leishmania major. J Exp Med 1993, 177:1505-1509. IL-12 administered systemically during the first week of I. major Infcc tion in BALB/c mice promoted control of lesions and parasites. This is the first study to demonstrate that qtokine thcr;lpy c’an posltnrh intluence the outcome of a leishmanial infection.
22.
HEINZEL FP,
.
JP, CHUNG CL, MAYORSEI I, SLI~KA,%~Y&\~ Jhl, G(x.IJ%!.%\ SJ, SIER~IR~HDS, WOI.F SF, SC~TAI;RRG Resolution of Cuta neous Leishmaniasis: lnterleukin 12 Initiates a Protective Thl Immune Response. J EQ ‘Weed1993. in press. Describes results that are similar to those reported in thr stud>. ,)t IIeinzel el al. [22-l: IL~l2 can be protective when administcrcd at the time of L. mujor infection in BALB/c mice. The study ,also indicates that treatment of resistant mice with anti~IL 12 polyclonal antiserum cn hances disease. 23. .
24. .
SYPEK
BARR&NET~O M, BARRAL A, BROWNELL CE. SKEIKY YAW. ELLINGSWORTH IR, TWARDZIK DR, REED SG. Transforming Growth Factor-P in Leishmanial Infection: A Parasite Escape Mechanism. Science 1992, 257:545-548. This study shows that TGF-P contributes to the suscepubility of BALB c mice to infection with L amazonensis When mice were treated v&h anti-TGF-P mAb they were partially protected. In contrast, when TGF-P was administered with the parasite L. hrazilie?zsis, which normal& causes no disease in mice, lesion development wan observed.
529
530
Immunity to infection BARRAL A, BARRAI-NETTO M, YONG EC, BROWNELL CE, ‘IWARDZIK D, REEDSG: Transforming Growth Factor-P as a Virulence Mechanism for Leisbmania braziliensis. Proc Nat Acad Sci USA 1993, 90:3442-3446. In this paper, the authors demonstrate that macrophages infected with L braziliensisproduced active TGF-/3,and the amount produced correlated directlywith in vivovirulence. Of interest, quiescent L braziliensis infections were turned into active lesions by local administration of TGF-p. Exacerbation of infection by TGF-fl was associated with increased levels of IL~lOin the draining lymph node. 25.
35.
.
26. .
MORRISL, TROU?T AB, HANDMAN E, KELSOA: Changes in the Precursor Frequencies of IL-4 and IFN-y Secreting CD4+ Ceils Correlate with Resolution of Lesions in Murine Cutaneous Leishmaniasis. J Immunol 1992, 149:2715-2721. This paper shows that following infection of C57BI/6 mice both Thl and Th2 cells are present during the first few weeks of infection. Only after 2 weeks do Thl cells dominate, suggesting that a delayed mechanism exists which selects this phenotype. 27.
WIU 4 BUWK C, ROLLINGHOFF M, MOLL H: Murine Epidermal Langerhans Cells are Potent Stimulators of an Antigen-specific T CelI Response to Leishmania major, the Cause of Cutaneous Leishmaniasis. EurJ Immunoll992, 22:1341-1347.
28.
BLANKC, FUCHSH, MPERSBERGERK, ROLLINGHOFF M, MOLLH: Parasitism of Epidermal Langerhans Ceils in Experimental Cutaneous Leishmaniasis with Leisbmania major J Infect Dis 1993, 16741-25. In this manuscript, the authors demonstrate that Iangerhans cells are parasitized following infection with L major, thus implicating this antigen-presenting cell as a component in the initiation of an immune response M)leishmaniasis. .
KAYE PM, COOKE A, LUNDT, WAlTE M, BLACKWELL JM: AItered Course of Visceral Leishmaniasis in Mice Expressing Transgenic I-E Molecules. Eur J Immunoll992, 22:357-364. The course of L donovani infection in mice lacking the I-E region of the MHC (NOD mice) and NOD mice in which the I-E gene had been transgenically introduced was compared. The introduction of the I-E region of the MHC enhanced parasite growth, suggesting that differences at the level of antigen presentation may inlluence disease. 29. .
30.
KWAN WC, MCMA.!XERWR, WONG N, REINERNE: Inhibition of Expression of Major Histocompatibility Complex Class II Molecules in Macrophages Infected with Lefshmania donovani Occurs at the Level of Gene Transcription Via a Cyclic AMP-independent Mechanism. Infect Immun 1992, 60:2115-2120.
31.
FRUTHU, Souoz N, LOUISJ: Leishmania major Interferes with Antigen Presentation by Infected Macrophages. J Immunol 1993, 150:1857-l%&
32. .
REINER SL, WANGZ-E, HATAMF, SCOTT P, I~CKSLEYRM: Com-
mon Lineage of Thl and Th2 Subsets in Leishmaniasis. Science 1993, 259:1457-1460. In this manuscript the authors find that following infection with L. major mice exhibit a preferential usage of the Vo4, V,8 TCR. T-cell clones and hybridomas were isolated that utilize this TCR, and which have either the Thl or Th2 cytoklne phenotype. This study suggests that differences ln the dominance of Thl and Th2 cells is probably not related to recognition of dierent leishmanial antigens. 33.
34.
Pathogenesis 36. .
CACERES-DI’ITMAK G, TAP~A FJ, SANCHEZMA, YAMAMURAM, UVEMURAK, MODLIN RL, BUX)M BR, CONMT J: Detefmi-
nation of the Cytokine Profile in Leishmaniasis Using the Polymerase Exp Immunol 1993, 91:5C&505. These authors demonstrated that Th2 cytokines cosal lesions and in half of diffuse cutaneous weakly expressed in cutaneous lesions. 37.
American Cutaneous Chain Reaction. Clin were expressed in mulesions, but were only
ZW~NGENBERGER K, HARMSG, PEDROSA C, OMENAS, SANDKAMP B, NEIFERSK: Determinants of the Immune Response in
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KARP CL, El.-SAJISH, W~NN TA, SATI MMH, KORD~JANI HM, HA.!.HIMFA, HAG-AU M, NEVA FA, NUTMANTB, SACKSDL: In
Vivo Cytokine Profiles in Patients with Kala-azar. Marked Elevation of Both Interleukin 10 and Interferon-y. J Clin Invest 1993, 91:1644-1648. mRNAs encoding both IL-10 and IFN-y are present in bone marrow from kala-azar patients. GHAUB HG, PIWE~AM MR, SKEIKVYAW, SIDDIGM, HA~HIM FA, EL-HASSAN AM, Russo DM, REEDSG: Interleukin 10 Production Correlates with Pathology in Human Leisbmania Infections. J Clin Invest 1993, in press. donovani IL-10 mRNA was elevated in lymph nodes from patients with acute visceral leishmaniasis, and returned to negative levels following treatment. In contrast, IFN-y mRNA was elevated in samples from both acutely infected and convalescent patients PBMCs responded to leishmanial antigen in vitro by the production of IL-10 mRNA, IL-10 was able to 39. .
downregulate antigen-specific PBMC responses, and anti-IL-10mAb was able to restore proliferative responses to PBMCs from acutely infected patients 40.
BARRAI-NETTO M, BARRAL A, SANTOSSB, CARV~O EM, BADARO R, ROCHAH, REEDSG, JOHNSONWD JR: Soluble IL-2 Receptor as an Agent of Serum-mediated Suppression in Human Visceral Leishmaniasis. J Immunol 1991, 147~281-284.
41.
VITALE G,
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RA~IUDDIN S, TELMA%NIAW, EL-AWADMEH, AI-AMARI0, ALJANADIM: y6 T Cells and the Immune Response in Visceral
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